In recent years, a large-capacity smart card has been developed along with higher requirements on an operating speed, a capacity and an interface speed of a smart card as well as the use of the smart card to provide a user with a more variety of services. As compared with a normal smart card, the large-capacity smart card has its CPU (Central Processing Unit), RAM (Random Access Memory). EEPROM (Electrically Erasable Programmable Read-Only Memory), counter and secured processing device unchanged and also the roles and locations of its profile and pins unchanged except an extra large-capacity Flash memory in addition to the original smart card chip, e.g., a nonvolatile NAND flash memory or a nonvolatile NOR flash memory for storage of codes and data.
The NOR flash memory and the NAND flash memory are two predominant types of nonvolatile flash memories at present. The NOR flash memory is characterized by XIP (eXecute In Place) where an application can be run directly in the flash memory without fetching codes into a system RAM. The NOR flash memory is efficient with transmission and has a very high cost benefit with a capacity of 1 to 4 MB but has its performance degraded by lower writing and erasing speeds. The NAND flash memory can offer an extremely high density of elements and reach a high storage density and also has high writing and erasing speeds but suffers from a drawback of its application arising from a special system interface required for management of the flash memory.
Both the NOR flash memory and the NAND flash memory are characterized by their large capacities and thus currently have been widely used in large-capacity smart cards, generally in a digital electronic product, an SD card (Secure Digital Memory Card), an SIM (Subscriber Identity Module) card inside a mobile phone terminal, etc., to provide effectively these devices with a sufficient storage capacity available to various applications, data, files, etc.
At present, a device-card interface between the smart card in use and the device where the smart card is located is at a voltage typically in support of three levels, 5V, 3V and 1.8V respectively, corresponding to three levels of voltage, and also carries limited current. Taking the SIM card in the mobile phone terminal as an example, the device-card interface of the mobile phone terminal to the SIM card carries current of no more than 15 mA, or 20 mA taking some redundancy into account, under a normal operating condition, and the mobile phone terminal may get abnormal with the current of the device-card interface going beyond the limit, for example, the mobile phone may be forced to be powered off so as to be protected against an abnormality attack.
However for the large-capacity smart card, the current of the device-card interface may be larger than that of the normal smart card due to the characteristic of performing a data erasing and writing operation on the large-capacity memory therein, and results of a test in which 1-byte random numbers were written into the NAND flash memory in the smart card in an Update Binary instruction by way of example showed that the average spike current of the device-card interface reached 23 mA while erasing and writing the data from and to the NAND flash memory, the current of the device-card interface ranged from 6 mA to 10 mA while running another application instead of erasing and writing the data from and to the NAND flash memory, and the current of the device-card interface was approximately 2 mA while the smart card was idle. As can be apparent from the results of the test, the current of the device-card interface was beyond the normal current range while performing the data erasing and writing operation on the NAND flash memory so that the mobile phone terminal became abnormal, and such significant current also had more battery power of the mobile phone terminal consumed and hence a standby period of time of the mobile phone terminal shortened.